PALO ALTO, Calif./WASHINGTON Treasury Secretary Timothy Geithner vowed on Monday that the United States would not devalue the dollar for export advantage, saying no country could weaken its currency to gain economic health.

"It is not going to happen in this country." Geithner told Silicon Valley business leaders of devaluing the dollar.

Geithner broke his silence on the dollar's protracted slide ahead of this weekend's meeting of finance leaders from the Group of 20 wealthy and emerging nations in South Korea, where rising tensions over Chinese and U.S. currency valuations are expected to take center stage.

"It is very important for people to understand that the United States of America and no country around the world can devalue its way to prosperity, to (be) competitive," Geithner added. "It is not a viable, feasible strategy and we will not engage in it."

Answering audience questions before the Commonwealth Club of California in Palo Alto, he said the United States needed to "work hard to preserve confidence in the strong dollar."

Geithner, normally reluctant to publicly discuss currency and market movements, has not uttered the so-called "strong dollar mantra" -- a refrain he helped create at Treasury in the 1990s -- since February.

On Friday, the dollar index hit a 10-month low against a basket of major currencies, while the greenback has been plumbing fresh 15-year lows against Japan's yen .

Many emerging market countries are complaining that Fed money creation is weakening the dollar, and causing more funds to flow into their markets, pushing up their currencies.

Talk of a "currency war" has persisted as countries take action to keep from losing export competitiveness.

Brazil on Monday moved to cool a strong rally in its currency by raising taxes for foreigners buying local bonds and trading in foreign exchange derivatives.

Finance Minister Guido Mantega said the move was aimed at reducing foreign investment into Brazil, and he urged other countries to take coordinated action against the weak dollar.

Argentina's Minister of Economy and Public Finance Amado Boudou on Monday called on developed nations to focus on creating jobs rather than actions that weaken their currencies, saying a "true currency war" was underway.

U.S. POINTS TO CHINA

The G20 finance ministers and central bank governors at the meetings in Gyeongju, South Korea are expected to tackle head-on the disparities in currency policies that are distorting capital flows in the hopes of achieving a more coordinated approach.

But U.S. officials have put most of the blame on China's highly restrictive exchange rate regime, which until recently had kept the yuan largely pegged to the dollar. The United States is pressuring China to allow the value of its yuan to rise to take some pressure off capital flows and to rebalance its economy away from exports.

On Friday, however, Geithner delayed a report about whether the yuan's value is being manipulated, saying instead that he wants to work through the G20 process to hash out a multilateral solution.

Geithner said in Palo Alto that he believes China will continue to lift the value of its yuan currency to aid the rebalancing of its economy away from exports and toward domestic growth.

Asked how much higher China should allow the yuan to rise, Geithner said: "Higher."

"You can't know how far it should go. What you know now is that it's significantly undervalued which I think they acknowledge and it's better for them, and of course very important for us, that it move. And I think it's going to continue to move," Geithner said.

However, his remarks did not square with an official Chinese state newspaper that reported the accelerated pace of yuan appreciation in recent weeks will not last long because China's trade surplus will soon peak.

Beijing has allowed its currency to rise about 2.8 percent since ending a 23-month peg to the dollar in June, with most of that rise coming since August.

Geithner said the delay in the report was an acknowledgment of the faster pace of yuan appreciation and we'd like to see that sustained."

At the G20 meetings in Gyeongju and a November leaders summit in Seoul, Geithner said he wanted to "maximize the chance that we can mobilize broader international support behind a set of improvements to the exchange rate policies of China and other emerging economies.

Asked if the dollar would lose its status as the world's reserve currency, the Treasury chief said, "not in our lifetime."

To do this, Geithner said the United States must maintain growth, but also demonstrate that it can restore budget discipline and improve its long-run fiscal prospects.

(Additional reporting by Samantha Pearson and Aluisio Alves in Sao Paulo, Hilary Burke and Magdalena Morales in Buenos Aires, and Langi Chiang and Simon Rabinovitch in Beijing; Writing by David Lawder; Editing by Diane Craft and Carol Bishopric)

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